/* $Id: html_write.pl,v 1.12 2002/02/01 15:04:52 jan Exp $ Part of XPCE --- The SWI-Prolog GUI toolkit Author: Jan Wielemaker and Anjo Anjewierden E-mail: jan@swi.psy.uva.nl WWW: http://www.swi.psy.uva.nl/projects/xpce/ Copyright (C): 1985-2002, University of Amsterdam This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(html_write, [ page/3, % generate an HTML page page/4, % page from head and body html/3, % Useful primitives for expanding html_begin/3, % +EnvName[(Attribute...)] html_end/3, % +EnvName html_quoted/3, % +Text html_quoted_attribute/3, % +Attribute % Emitting the HTML code print_html/1, % +List print_html/2, % +Stream, +List html_print_length/2 % +List, -Length ]). :- use_module(library(quintus)). % for meta_predicate/1 :- meta_predicate html(:, -, +), page(:, -, +), page(:, :, -, +), pagehead(:, -, +), pagebody(:, -, +). /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - library(html_write) The purpose of this library is to simplify writing HTML pages. Of course, it is possible to use format/[2,3] to write to the HTML stream directly, but this is generally not very satisfactory: * It is a lot of typing * It does not guarantee proper HTML syntax. You have to deal with HTML quoting, proper nesting and reasonable layout. * It is hard to use satisfactory abstraction This module tries to remedy these problems. The idea is to translate a Prolog term into an HTML document. We use DCG for most of the generation. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */ page(Content) --> [ '\n', '', nl(1) ], html(Content), [ nl(1), '\n' ]. page(Head, Body) --> [ '\n', '', nl(1) ], pagehead(Head), pagebody(Body), [ nl(1), '\n' ]. pagehead(Head) --> { strip_module(Head, M, _), hook_module(M, head(_,_,_)) }, !, M:head(Head). pagehead(Head) --> html(head(Head)). pagebody(Body) --> { strip_module(Body, M, _), hook_module(M, body(_,_,_)) }, !, M:body(Body). pagebody(Body) --> html(body([bgcolor(white)], Body)). hook_module(M, P) :- current_predicate(_, M:P), !. hook_module(user, P) :- current_predicate(_, user:P). html(Spec) --> { strip_module(Spec, M, T) }, html(T, M). html([], _) --> !, []. html([H|T], M) --> !, ( do_expand(H, M) -> [] ; { print_message(error, html(expand_failed(H))) } ), html(T, M). html(X, M) --> do_expand(X, M). :- multifile expand/3. do_expand(Token, _) --> % call user hooks expand(Token), !. do_expand(Fmt-Args, _) --> !, { sformat(String, Fmt, Args) }, html_quoted(String). do_expand(\List, _) --> { is_list(List) }, !, List. do_expand(\Term, Module, In, Rest) :- !, call(Module:Term, In, Rest). do_expand(Module:Term, _, In, Rest) :- !, call(Module:Term, In, Rest). do_expand(script(Content), _) --> !, % general CDATA declared content elements? html_begin(script), [ Content ], html_end(script). do_expand(&(Entity), _) --> !, { concat_atom([&, Entity, ;], HTML) }, [ HTML ]. do_expand(Token, _) --> { atomic(Token) }, !, html_quoted(Token). do_expand(element(Env, Attributes, Contents), M) --> !, html_begin(Env, Attributes), html(Contents, M), html_end(Env). do_expand(Term, M) --> { Term =.. [Env, Contents] }, !, ( { layout(Env, _, empty) } -> html_begin(Env, Contents) ; html_begin(Env), html(Contents, M), html_end(Env) ). do_expand(Term, M) --> { Term =.. [Env, Attributes, Contents] }, !, html_begin(Env, Attributes), html(Contents, M), html_end(Env). html_begin(Env) --> { Env =.. [Name|Attributes] }, html_begin(Name, Attributes). html_begin(Env, Attributes) --> pre_open(Env), [<], [Env], attributes(Attributes), [>], post_open(Env). html_end(Env) --> % empty element or omited close { layout(Env, _, -) ; layout(Env, _, empty) }, !, []. html_end(Env) --> pre_close(Env), [''], post_close(Env). attributes([]) --> !, []. attributes([H|T]) --> !, attribute(H), attributes(T). attributes(One) --> attribute(One). attribute(Name=Value) --> !, [' ', Name, '="' ], html_quoted_attribute(Value), ['"']. attribute(Term) --> { Term =.. [Name, Value] }, !, attribute(Name=Value). attribute(Atom) --> % Value-abbreviated attribute { atom(Atom) }, [ ' ', Atom ]. /******************************* * QUOTING RULES * *******************************/ % html_quoted(Text) % % Quote the value for normal text. html_quoted(Text) --> { sub_atom(Text, _, _, _, <) ; sub_atom(Text, _, _, _, >) ; sub_atom(Text, _, _, _, &) }, !, { atom_chars(Text, Chars), quote_chars(Chars, QuotedChars), concat_atom(QuotedChars, Quoted) }, [ Quoted ]. html_quoted(Text) --> [ Text ]. quote_chars([], []). quote_chars([H0|T0], [H|T]) :- quote_char(H0, H), quote_chars(T0, T). quote_char(<, '<') :- !. quote_char(>, '>') :- !. quote_char(&, '&') :- !. quote_char(X, X). % html_quoted_attribute(+Text) % % Quote the value according to the rules for tag-attributes html_quoted_attribute(Text) --> { sub_atom(Text, _, _, _, <) ; sub_atom(Text, _, _, _, >) % ; sub_atom(Text, _, _, _, &) ; sub_atom(Text, _, _, _, '"') % ; sub_atom(Text, _, _, _, '''') }, !, { atom_chars(Text, Chars), quote_att_chars(Chars, QuotedChars), concat_atom(QuotedChars, Quoted) }, [ Quoted ]. html_quoted_attribute(Text) --> [ Text ]. quote_att_chars([], []). quote_att_chars([H0|T0], [H|T]) :- quote_att_char(H0, H), quote_att_chars(T0, T). quote_att_char(<, '<') :- !. quote_att_char(>, '>') :- !. %quote_att_char(&, '&') :- !. quote_att_char('"', '"') :- !. %quote_att_char('''', ''') :- !. quote_att_char(X, X). /******************************* * LAYOUT * *******************************/ pre_open(Env) --> { layout(Env, N-_, _) }, !, [ nl(N) ]. pre_open(_) --> []. post_open(Env) --> { layout(Env, _-N, _) }, !, [ nl(N) ]. post_open(_) --> []. pre_close(Env) --> { layout(Env, _, N-_) }, !, [ nl(N) ]. pre_close(_) --> []. post_close(Env) --> { layout(Env, _, _-N) }, !, [ nl(N) ]. post_close(_) --> []. % layout(Tag, PreOpen-PostOpen, PreClose-PostClose) % % Define required newlines before and after tags. This table is % rather incomplete. :- multifile layout/3. layout(table, 2-1, 1-2). layout(blockquote, 2-1, 1-2). layout(center, 2-1, 1-2). layout(dl, 2-1, 1-2). layout(ul, 2-1, 1-2). layout(form, 2-1, 1-2). layout(frameset, 2-1, 1-2). layout(head, 1-1, 1-1). layout(body, 1-1, 1-1). layout(script, 1-1, 1-1). layout(select, 1-1, 1-1). layout(map, 1-1, 1-1). layout(html, 1-1, 1-1). layout(tr, 1-0, 0-1). layout(option, 1-0, 0-1). layout(li, 1-0, 0-1). layout(dt, 1-0, -). layout(dd, 0-0, -). layout(title, 1-0, 0-1). layout(h1, 2-0, 0-2). layout(h2, 2-0, 0-2). layout(h3, 2-0, 0-2). layout(h4, 2-0, 0-2). layout(hr, 1-1, empty). % empty elements layout(br, 0-1, empty). layout(img, 0-0, empty). layout(meta, 1-1, empty). layout(base, 1-1, empty). layout(link, 1-1, empty). layout(input, 0-0, empty). layout(frame, 1-1, empty). layout(col, 0-0, empty). layout(area, 1-0, empty). layout(input, 1-0, empty). layout(option, 1-0, empty). layout(p, 2-1, -). % omited close layout(td, 0-0, 0-0). /******************************* * PRINTING * *******************************/ % print_html(+Stream, +List) % % Print list of atoms and layout instructions. Currently used layout % instructions: % % nl(N) Use at minimum N newlines here. print_html(List) :- current_output(Out), write_html(List, Out). print_html(Out, List) :- write_html(List, Out). write_html([], _). write_html([nl(N)|T], Out) :- !, join_nl(T, N, Lines, T2), write_nl(Lines, Out), write_html(T2, Out). write_html([H|T], Out) :- write(Out, H), write_html(T, Out). join_nl([nl(N0)|T0], N1, N, T) :- !, N2 is max(N0, N1), join_nl(T0, N2, N, T). join_nl(L, N, N, L). write_nl(0, _) :- !. write_nl(N, Out) :- nl(Out), N1 is N - 1, write_nl(N1, Out). % html_print_length(+List, -Len) % % Determine the content length of the list. html_print_length(List, Len) :- html_print_length(List, 0, Len). html_print_length([], L, L). html_print_length([nl(N)|T], L0, L) :- !, join_nl(T, N, Lines, T1), L1 is L0 + Lines, % assume only \n! html_print_length(T1, L1, L). html_print_length([H|T], L0, L) :- atom_length(H, Hlen), L1 is L0+Hlen, html_print_length(T, L1, L). /******************************* * MESSAGES * *******************************/ :- multifile prolog:message/3. prolog:message(html(expand_failed(What))) --> [ 'Failed to translate to HTML: ~p'-[What] ].